fix cherry-pick leftovers

Author: SzyWilliam

ratis-server/src/main/java/org/apache/ratis/server/impl/RaftServerImpl.java

@@ -118,7 +118,6 @@
 import java.nio.file.NoSuchFileException;
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.Comparator;
 import java.util.List;
 import java.util.Map;